The present invention relates generally to procedures known as cloth welding and more particularly to devices to weld together sheets of thermoplastic materials by the use of ultrasonic vibration equipment.
The products so produced are suitable for many uses such as upholstery material, blankets, tablecovers, sleeping bags and many other articles. Apparatus for ultrasonically welding thermoplastic materials are well known in the art for producing seams and overlapping edges of one material to another. One example of such a device is shown in U.S. Pat. No. 3,733,238--Long, et al. In general, the elements to be joined are located between an ultrasonically vibrating member having an elongate working surface and a back up anvil means having raised surfaces located in the desired area of the weld. The anvils are heated by the ultrasonic transmitter to weld the sheets of material together in the area of the anvil. In many applications the anvils are carried on the surface of a drum which is rotated with the feed of the materials to be joined and extend outwardly therefrom to be sequentially located beneath the transmitter as the drum turns. Insofar as presently known, the prior art teaches a single drum carrying anvils where multiple transmitters are provided in staggered orientation.
In general the width of the vibration transmitting members is a limitation on the width of the material which can be joined. However, by the use of numerous vibration transmitting members, full width fabrics can be joined. The vibration transmitting members cannot be in contact with each other but by proper placing of the anvils and by overlapping of the vibrating transmitting means full width transmitting means full width patterns can be produced.
In welding of cloth material the clearance between the vibration transmitting device and the anvils is critical. For example, a 0.001 inch clearance is desirable between the anvil and the vibration transmitting device and the tops of the anvils should be flat to provide uniform clearance. The power required to be applied to the vibration transmitting device to accomplish welding is dependant upon the clearance between the anvil and the transmitting device and the mass of the anvils. In prior art devices it has been necessary to maintain uniform clearance between the anvil and the transmitter and further in prior art devices using solid anvils, it is necessary to always have the same number of anvils exposed to the transmitter because if fewer anvils are present the total power of the transmitter is utilized by the fewer number of anvils and overheating and burn through occurs so a hole is formed. On the contrary, if more than the requisite number of the prior art anvils are located beneath the transmitter the power is insufficient to properly heat the anvils so welding does not occur.
Prior art devices have generally provided solid, for example, circular, anvils or solid elongate anvils.
No prior art device is known where a semi-enclosed anvil is utilized using substantially less mass in an anvil whereby the weld strength is improved and the likelihood of "burn through" is substantially reduced.